A preferred application for the present invention is in high voltage alternating current (AC) circuit breakers and reclosers, the latter being a type of circuit breaker. Therefore, the background of the invention is described below in connection with such devices. However, it should be noted that, except where they are expressly so limited, the claims at the end of this specification are not intended to be limited to applications of the invention in high voltage AC circuit breakers or reclosers.
A high voltage circuit breaker is a device used in the distribution of three phase electrical energy. When a sensor or protective relay detects a fault or other system disturbance on the protected circuit, the circuit breaker operates to physically separate current-carrying contacts in each of the three phases by opening the circuit to prevent the continued flow of current. A recloser differs from a circuit breaker in that a circuit breaker opens a circuit and maintains the circuit in the open position indefinitely, whereas a recloser may automatically open and reclose the circuit several times in quick succession to allow a temporary fault to clear and thus, avoid taking the circuit out of service unnecessarily.
A major component of a circuit breaker or recloser is an interrupter. Typically, a circuit breaker will include one or more interrupters which function to open and close one or more sets of current carrying contacts housed within the interrupter. A longitudinal cross section of an interrupter 10 is shown in FIGS. 1, 2, and 3. The interrupter 15 shown within a housing 30. A movable contact system 11 and a stationary contact system 13 are shown to have two sets of contacts, the arcing contacts 12 and 14 and the main contacts 15 and 19, respectively. The stationary contact system is typically mounted to the housing 30. The movable contact system 11 is operationally connected to a driving mechanism of the circuit breaker (not shown) which can cause the movable contact system to move along the contact support 20 to open and close the circuit breaker. The contact support 20 surrounds the exhaust tube 26 :which is operatively connected to housing 30. Arcing contact 12 and main contact 19 of the movable contact system are moved along the contact support 20 to either close the circuit with respective contacts 14 and 15 or to open the circuit, FIG. 1 shows a longitudinal cross sectional view of the interrupter with its contacts closed, whereas FIG. 3 shows a longitudinal cross section of the interrupter with the contacts open.
The arcing contacts 12 and 14 of high voltage circuit breaker interrupters are subject to arcing or corona discharge when they are opened or closed, respectively. As shown in FIG. 2, an arc 16 is formed between arcing contacts 12 and 14 as they are moved apart. Such arcing can cause the contacts to erode and perhaps to disintegrate over time. Therefore, a known practice (used in a "puffer" interrupter) is to fill a cavity of the interrupter with an inert, electrically insulating gas that quenches the arc 16. As shown in FIG. 2, the gas is compressed by piston 17 and a jet or nozzle 18 is positioned so that, at the proper moment, a blast of the compressed gas is directed toward the location of the arc in order to extinguish it. Once an arc has formed, it is extremely difficult to extinguish it until the arc current is substantially reduced. Once the arc is extinguished, the protected circuit is opened, as shown in FIG. 3, to prevent current flow.
When the interrupter is opened as shown in FIG. 2, hot gases are formed. If the hot gases are permitted to pass through the interface between the movable and stationary contact systems and enter the region of the main contacts 15 and 19, the interrupter can fail. Therefore, the nozzle 28 of the movable contact system must provide a good seal with the stationary contact system 13.
Another cause of contact erosion results from the movement of the contacts against one another as the interrupter is opened and closed. To reduce contact erosion caused by the movement of the contacts, it is desirable to stabilize the alignment between the contacts of the movable contact system and the contacts of the stationary contact system while the movable contact system is guided along the contact support to open the circuit. If the contacts are not aligned to provide a stable interface therebetween, they may erode quicker or become damaged by excessive contact pressure at the interface.
A guidance system comprising two guides 22 and 24 is typically utilized to improve the stability of the alignment between the movable contact system and the stationary contact system. The first guide is typically inserted between the contact support 20 and the movable contact system 11 as shown in FIGS. 1, 2 and 3. The second guide 24 is typically inserted between the contact support 20 and the exhaust tube 26. The first guide 24 fills in any gaps between the movable contact system 11 and the contact support 20 so that the movable contact system 11 has a more stable alignment with the contact support 20. Similarly, the second guide 24 secures exhaust tube 26 and the contact support 20 so that the contact support 20 remains fixed during the interrupter operation.
In order to provide a stable alignment between the movable contact system and the stationary contact system, the stationary contact system is usually mounted to the housing 30 so that the movable and stationary contact systems are critically aligned. Traditionally, a person assembling the interrupter aligns the movable and stationary contact system manually using a trial and error process. Determining this critical alignment manually is both time consuming and subject to error. Moreover, even when the critical alignment is determined in such a manner, error may be introduced during the mounting of the stationary contact system itself.
A stable alignment between the stationary contact system 13 and the movable contact system 11 is desired to maintain the electrical integrity of the switch or circuit breaker. An electrical field is formed between the nozzle 28 and the main contact 15 of the stationary contact system. When the interrupter is in the open position, a misalignment between the movable contact system and the stationary system increases the electric field stress and increases the risk of flashover.
Therefore, there is a need for a guidance system capable of providing a self-adjusting stable alignment between the movable contact system and the stationary contact system in an interrupter.